1. Field of the Invention
This invention relates in general to liquid level responsive sending units adapted for disposition within fuel tanks and particularly relates to a sending unit that emits an electronically damped fuel level signal from within an automobile or truck fuel tank.
2. Description of Prior Developments
Fuel tank liquid level sensors or sending units commonly include a mounting structure or base located at an intermediate point within a fuel tank, i.e. several inches above the floor of the tank. An arm structure is swingably mounted on the base for swinging motion in a vertical plane and carries a float at its free end. Typically, the arm structure has a length of about five inches, and it swings through a vertical arc of about eighty degrees when going from a lowered (tank empty) condition to a raised (tank full) condition.
This swingable arm structure carries an electrical slider. A cooperating potentiometric resistance is located on the base, such that vertical swinging motion of the float arm structure causes the slider to wipe and slide along the electric resistance, thereby generating an electrical signal related to the fuel liquid level in the tank, i.e. the level sensed by the float.
During certain operational periods of the vehicle, e.g. sudden braking, moving uphill or turning sharply, the fuel in the tank may slosh around or move toward one end of the tank. Momentarily, the float will sense a false liquid quantity, i.e. a liquid level that is not representative of the liquid quantity in the tank. This momentary condition will be sensed by the motorist as a fluttering motion of the fuel level indicator needle in the gage on the dashboard.
In order to minimize or eliminate undesired fluttering or wandering motion of the fuel level indicator needle, it has been proposed to provide an electrical damping circuit in the electrical system between the electrical sending unit in the tank and the electrical needle operator (coil) in the gage. U.S. Pat. Nos. 4,497,205 and 4,635,043 disclose damping circuits that have been proposed There are other circuits that can be used.
These damping circuits receive a fluctuating signal from the sending unit, and translate that signal into an essentially steady state signal that is representative of the average signal generated over a measurable time period, e.g. forty-five seconds or more. This average signal is the signal that is sent to the coil or coils in the fuel level indicator on the dashboard.
The damping circuits do not interfere with the accuracy or normal operation of the fuel level indicator system, since over time the signal sent to the gage reflects long term changes in the liquid fuel levels, i.e. changes requiring more than about a minute of vehicle operation.
It is believed that the damping circuits, when used, have been physically located somewhere in the vehicle dashboard. Present technology is such that wiring within the dashboard is often cluttered and complex, with a maze of wires occupying much of the space behind the dashboard.